The present invention relates to a projection display device such as a liquid crystal projector having a cooling fan. The invention more particularly relates to a technique for accurately detecting clogging of a dustproof filter on the basis of a reduction in the velocity of cooling air.
A projection display device such as a liquid crystal projector irradiates a display element such as a liquid crystal panel with light emitted by a light source such as a mercury lamp. The projection display device enlarges and projects an image that is formed by the display element through a projection lens onto a screen. The display element is irradiated with the light emitted by the light source and is heated so that the temperature of the display element increases. When the temperature of the display element excessively increases, the display element may be transformed or the quality of the image may be degraded. To cope with this, a cooling fan to blow cooling air to the display element is provided to suppress temperature increase in the display element.
In general, a flow path for cooling air is configured so that a suction fan draws air from outside of the device through an inlet into the device and then blows the air to the display element. In order to prevent dust and a foreign material that will enter from the inlet from being attached to the display element, a dustproof filter is attached to the inlet. However, when dust or a foreign material is accumulated on the dustproof filter to cause the dustproof filter to be clogged, the amount of air that is drawn into the device is reduced, and the cooling effect is reduced. This results in an increase in the temperature of the display element. To avoid this, the velocity of the cooling air that is to be blown to the display element is detected. When the velocity of the cooling air becomes equal to or lower than a set value due to clogging of the filter or the like, a power source for the display device is turned off to protect the display element.
A liquid crystal projector described in JP-A-11-84534 is configured as follows. Liquid crystal panels are formed so as to allow cooling air to flow along the surfaces of the liquid crystal panels and an air velocity sensor is arranged on an output portion (from which the cooling air flows through the liquid crystal panels and is output) in order to accurately measure the velocity or amount of the cooling air while suppressing an effect of air blown by an exhaust fan that is located on the back side of the liquid crystal panel.